[nostrademons]

I was also not in YT (was in Search from 09-14), but a bunch of my coworkers went over to work there around '10-11. I read the paper before joining Google; I think it came out in 07 or 08.

There might also be a lot of confusion over "backend" vs. "frontend" terminology. Like the other poster mentioned, "frontend" at Google usually means the webserver and sometimes extends back to various application-level services. Basically everything that involves user interaction. Experiment infrastructure has been part of the frontend in every system I've worked with at Google (which now includes Search, Google+, GFiber, Doodles, AndroidTV, and Assistant), though the flags often get plumbed back to backends to alter behavior there.

By "backend" I mean the storage & offline processing areas. BigTable, Colossus, MapReduce, various blob stores, training machine-learning models, etc. This is the part of YT that (in my understanding) was rewritten to use Google technologies.